1. Field of the Invention
This invention relates to the field of energy management systems and, in particular, to the field of energy management systems for buildings having a plurality of individually controlled spaces.
2. Prior Art
During normal operation of an air conditioner air is forced over a coil while the air conditioner is in operation in order to permit the coil to absorb thermal energy from the air thereby cooling the air. However, it is also known in the prior art to continue to blow air over the coil after operation of the air conditioner terminates until the coil reaches ambient temperature. This decreases wasted energy.
The energy management system and method of the present invention manages energy usage by an energy consuming system. The energy consuming system managed by management system and method of the present invention manages the energy consuming device by determining a plurality of parameters within the controlled space in order to reduce energy waste during heating and cooling of the controlled space. The controlled space can be one of a plurality of differing independently controllable spaces. For example, the controlled space can be a single room in a hotel wherein each such hotel room must be well controlled in order to avoid any periods of guest discomfort. Additionally, the control must be performed in a manner that does not cause any disturbance to an occupant of the controlled space.
For example, the present invention can determine the temperature settings of the controlled space as well as changes in temperature settings, or setbacks. Additionally, the hysteresis or span of the energy consuming device can be determined by the present invention. Furthermore, the energy management system of the present invention gives priority to the comfort of any occupants of the controlled space when controlling the energy usage of the controlled space since it is advantageously applied to buildings such as hotels where guest comfort is very important. The control logic of the system and method of the present invention can be applied to the various energy consuming devices of the controlled space on a priority basis.
The present invention can use parameters in addition to temperature settings in order to perform its control functions. For example, time of day, day of week, month, day of month, season of year, ingress and egress, window opening and closing, change in status, occupancy state, circadian rhythm of occupant, ambient noise level, light level, energy consumption, temperature drift rate and direction, rate of energy consumption, utility tariffs, humidity, and environment or weather can also be used in performing the control functions. The weather information can come, for example, from local weather instruments, data input, or the internet.
Additionally, by making use of card keys that can open a door of the controlled space it is possible to distinguish different types of individuals who enter the controlled space. For example, in a hotel it is possible to distinguish between guests and staff entering the controlled space according to the card key used. Therefore, occupant identification can also be used as system parameter in the present invention.
One way for the system of the present invention to increase the comfort level of the occupant of a controlled space is to reduce the perception of the noise coming from a heating, venting and air conditioning (HVAC) system. This is partly accomplished by reducing the frequency of the changes in the HVAC equipment noise levels. The frequency of the changes in HVAC noise levels can be reduced, for example, by increasing the control span of the energy consuming system managed by the system of the present invention.
Reduction of the noise perception of an occupant is also accomplished by reducing the changes in the noise levels of the HVAC equipment. The reduction in the changes in HVAC equipment noise level is obtained by masking the changes in noise levels created by on/off state transitions of the HVAC equipment. Masking the changes in noise level while the occupant is sleeping, and thereby reducing the noise perceived by the occupant, can cause the occupant to be awakened less frequently than with a standard on/off thermostatic control of the space.
The noise masking method of the present invention is effective to reduce the noise perceived by an occupant of the controlled space because individuals become accustomed to a constant level of ambient noise in a space they occupy. Noise sensitivity, or noise perception, by an individual can thus be related to the relative magnitude of changes in the ambient noise level once the individual becomes accustomed to a constant noise level. Greater changes in the noise level are more readily noticed by the individual than smaller ones.
Noise masking in accordance with the present invention can be advantageously performed any time that an occupant is present within the controlled space. Alternately, it can be performed only when the occupant is in the controlled space and is determined to be resting or sleeping. When the controlled space is unoccupied, or when the controlled space is occupied but the occupant is not resting or sleeping, the most energy efficient control method can take priority over noise reduction methods in order to reduce energy consumption.
In addition to providing further sleeping comfort using noise reduction, the method of the present invention enhances sleeping comfort using the natural circadian rhythm of the occupant. In this feature of the present invention changes in setback temperatures can be provided in accordance with the normal daily changes in the body temperature of the occupant. This feature of the present invention can also reduce energy consumption during occupied periods while adding to the comfort of the occupant and the ability of the occupant to sleep.
Additionally, the system and method of the present invention make use of ambient energy in controlling energy consumption within the controlled space. In order to perform this function the present invention is provided with an enthalpy system that can inhibit the use of any energy consuming devices. The enthalpy system inhibits the energy use when the measured natural direction of temperature change, or temperature drift, is the same as the desired direction of temperature change.
The system of the present invention determines the current natural direction of temperature change by repeatedly measuring the ambient temperature of the controlled space. This makes it possible to track the rate of temperature change as well as the direction of temperature change. If the natural direction of the ambient temperature change is the same as the desired direction, the system inhibits HVAC activation unless it is overridden by other predetermined conditions.
The determination to override the HVAC inhibit feature when the control direction and the natural direction are the same can be made according to many considerations. The considerations are mostly, but not exclusively, related to the comfort of the occupant. The override considerations can include occupancy of the controlled space, whether the occupant is in a rest or sleep state, the duration and rate of the ambient temperature change, and the time required to reach the desired temperature range using the natural temperature drift. Emergency conditions such as freezing and other predetermined emergencies can also be considered before inhibiting the HVAC equipment.
The system of the present invention establishes a band of control in addition to the span of control. The band of control can be selected to include or exclude the span of control and to extend predetermined amounts above and below the span of control. Furthermore, the band of control is determined by the logic of the energy management system of the present invention to save energy and to provide occupant comfort. When the controlled space is determined to be within the band of control no further energy is applied to the energy system unless an override condition exists.
Occupants of a controlled space can select heating or cooling of the controlled space. This is referred to as selecting the direction of control of the energy consuming system. The system of the present invention can reverse the direction of control if necessary to satisfy a temperature setting. However, the direction of control can be reversed after satisfying the thermostatic requirements set by the span of control and temperature setpoint. Furthermore, the direction of control can be reversed if the temperature continues to drift until it reaches an override setting. This is considered an override situation because the energy consuming system is acting to satisfy defined override parameters. Energy savings are not necessarily maximized when this occurs.
When the controlled space is unoccupied the direction of control is selected by the system of the present invention. Under these conditions the HVAC equipment is only activated under the following circumstances. When the temperature is within a broad temperature control band defined by the system of the present invention no energy whatsoever is applied to the energy consuming system. If the temperature drifts either to the extreme upper limit or to the extreme lower limit of the control band either the heater or the air conditioner of the occupied space can be activated. The selection of the direction of the energy consuming device selected depends upon which direction is required to return the temperature of the controlled space to the limits defined by the band of control.
The system of the present invention may determine an out-of-limit condition exists and that the natural drift is in the direction required to return the measured temperature to the control band. Under these circumstances the present invention continues to inhibit energy use if no override or emergency conditions are detected. Heat pump use can be maximized since the system of the present invention always provides heat pump operation whenever the controlled space is unoccupied and whenever the controlled space is occupied but use of the heat pump does not cause occupant discomfort.
The system and method of the present invention permits real time based adaptive self programming in order to select setback levels and comfort settings within the occupied space. Additionally, the present invention manages energy usage based upon calendar and time information stored therein. This permits more accurate approximation of the amount of energy usage and the manner of energy usage within the controlled space. It also permits prediction of the expected energy requirements for heating and cooling the controlled space. For example, energy utilization parameters of a property, such as billing rates, demand rates, consumption rate, occupancy patterns, sleep, housekeeping, maintenance, outdoor temperature and humidity, usage of other energy devices such as lights, solar heat gains, and other parameters can be used by the present invention to manage the energy consuming device and control the environment of the controlled space. All of these parameters can have a calendar and time dependent variation.